At the end of the Warring States period, Qin was a rich and powerful country. So the ambition of external expansion was revealed. At that time, the first target was South Korea. Compared with Qin at that time, South Korea's national strength was simply vulnerable. In order to survive, Koreans expressed their willingness to build large-scale irrigation projects for Qin at all costs. The person sent is an expert of Qin State, who has made great achievements in water conservancy and is called Zheng State.
But in fact, Zheng did not build this water conservancy project specifically for Qin. He is a spy, thinking that the state of Qin used building a canal as an excuse to delay time and consume the financial resources of the state of Qin. This large-scale irrigation project in Zheng Guoqu wasted people and money, so ten years have passed. Finally, the King of Qin discovered the purpose of the Koreans and wanted to execute the spy Zheng Guo.
In order to save his life, Zheng told the king of Qin the significance of building. It took the king of Qin a long time to hold back his anger, and he also understood that it was not worth the loss to give up halfway now. Zheng did not dare to delay deliberately, and carefully analyzed the construction situation. With the successful construction of this large-scale irrigation project, the economic level of Qin has also been improved. Although North Korea was later destroyed, it was called "Zheng Guoqu" because the construction of Zheng Guoqu was also of great significance.